Method of manufacturing a cylindrical part by fiber reinforced plastic composite material

ABSTRACT

The disclosed method can manufacture a thick-walled cylindrical part of an excellent quality which is free from the interlayer separation, by using a fiber reinforced plastic composite material. The fiber reinforced plastic composite material having a small thermal expansion coefficient is laminated in the circumferential direction of a mandrel; the laminated fiber reinforced plastic composite material layer is heat-cured to form an auxiliary member of the mandrel; a plurality of sorts of fiber reinforced plastic composite materials having a different elastic modulus, respectively are laminated on the formed auxiliary member; and the laminated fiber reinforced plastic composite materials are all heat-cured.

REFERENCE TO A RELATED APPLICATION

This application is a divisional application of parent application Ser.No. 08/870,419 filed Jun. 5, 1997, now U.S. Pat. No. 5,985,073 which isrelied on and incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cylindrical part manufactured byfiber reinforced plastic composite material so as to be used as astructural member, and a method of manufacturing the same cylindricalpart by fiber reinforced plastic composite material.

2. Description of the Related Art

The fiber reinforced plastic composite material is excellent in specificstrength, specific rigidity and corrosion resistance. However, therestill exist various technical problems to be solved when a structuralmember is manufactured by fiber reinforced plastic composite material.

When a thick-walled cylindrical part is manufactured by the fiberreinforced plastic composite material, various methods such as thefilament winding method, tape winding method, sheet winding method, andetc. are now being adopted.

However, the fiber reinforced plastic composite material is providedwith such characteristics that a thermal expansion coefficient thereofdiffers largely according to the lamination direction. Therefore, when athick-walled cylindrical part is manufactured by the fiber reinforcedplastic composite material, internal stress proportional to a differencebetween the curing temperature and room temperature is inevitablygenerated in the fiber reinforced plastic composite material, afterbeing heated for curing. In the case of the thick-walled cylindricalpart, there exists the case where the internal stress generated in thefiber reinforced plastic composite material exceeds an interlayerbonding strength of the fiber reinforced plastic composite material. Inthis case, an interlayer separation occurs in the fiber reinforcedplastic composite material.

In a general laminating process of thick-walled cylindrical parts, manylamination angles of ±10°/±45°/±85° are combined with each other. Inthis case, when a diameter of the cylindrical part is small (e.g., lessthan 200 mm) and the wall thickness is large (e.g., more than 30 mm),since the internal stress becomes excessively large, there exists aproblem in that the interlayer separation occurs.

To overcome this problem related to the interlayer a separation,Japanese Published Unexamined (Kokai) Patent Application No. 2-236014discloses such a method of laminating a layer strengthened againsttorsion (of which the lamination angle is ±30° to ±60° with respect tothe axial direction) and the layer strengthened against bending (ofwhich the lamination angle is 0° to 20°) alternately, in order tosuppress the interlayer separation due to a difference in the thermalexpansion coefficient between the conditions when heated for curing andwhen cooled to the room temperature.

Further, Japanese Published Unexamined (Kokai) Patent Application No.6-335973 discloses a method of using high frequency induction heatingmeans, to reduce the temperature dispersion while heating for curing andthereby to decrease the internal stress thereof.

In the first prior art method of laminating plies at differentlamination angles (i.e. directions), since the wall thickness of themanufacturable cylindrical parts is limited to about 15 mm, when thewall thickness thereof increases more than this value (e.g., 15 to 50mm), the internal stress generated in the fiber reinforced plasticcomposite material sharply increases with increasing wall thickness, sothat the interlayer separation occurs in the fiber reinforced plasticcomposite material layers. Therefore, it is impossible to manufacture acylindrical structure of high strength and high rigidity by making thebest use of the characteristics of the composite material.

Further, in the second prior art method of using a high frequencyinduction heating apparatus in order to reduce the temperaturedispersion during the heat curing and thereby to reduce the internalstress generated in the fiber reinforced plastic composite materiallayers, since magnetic substances are added to the matrix resin, theweight thereof inevitably increases, and as the result there exists aproblem in that the weight of the structural body is increased andfurther the performance of the structural body is degraded. In thismethod, additionally there exists another problem in that a special highfrequency induction heating facility must be prepared in accordance withthe shape of the manufactured structural body, instead of an autoclaveor a heating furnace.

Further, when a mandrel formed of steel (thermal expansion coefficient:10 to 12×10⁻⁶/°C. ) is used, since the mandrel is shrunk when cooledafter heat curing, there exists a problem in that the inside layers areshrunk in the radial direction thereof and thereby the interlayerseparation often occurs.

SUMMARY OF THE INVENTION

With these problems in mind, therefore, it is an object of the presentinvention to provide a method of manufacturing a thick-walled (e.g., 40mm) cylindrical part having a stable quality by use of fiber reinforcedplastic composite material, by reducing the internal stress thereof,while using conventional equipment.

To achieve the above-mentioned object, the present invention provides amethod of manufacturing the cylindrical part by fiber reinforced plasticcomposite material, which includes the step of laminating a fiberreinforced plastic composite material with an elastic modulus on amandrel, winding a different kind of said composite material withanother elastic modulus on said fiber reinforced plastic compositematerial, repeating alternately said laminating and said winding, curingboth of said materials, and deriving a fiber reinforced plastic productwithout deformation due to internal stress after cooling down and takingout said mandrel.

Further, the present invention provides a method of manufacturing thecylindrical part by the fiber reinforced plastic composite material,comprising the steps of: laminating a fiber reinforced plastic compositematerial having a small thermal expansion coefficient in acircumferential direction of a metallic mandrel; heating the laminatedfiber reinforced plastic composite material for curing, to form anauxiliary member; laminating another fiber reinforced plastic compositematerial on an outer side of the formed auxiliary member; and heatingthe formed laminated fiber reinforced plastic composite material forcuring.

Further, the present invention provides a method of manufacturing athick-walled cylindrical part by fiber reinforced plastic compositematerial, comprising the steps of: laminating a fiber reinforced plasticcomposite material having a small thermal expansion coefficient in acircumferential direction of a mandrel; heat-curing the laminatedcomposite material under first heating conditions to form an auxiliarymember; covering the formed auxiliary member with a thin film of highheat resistance; laminating another fiber reinforced plastic compositematerial on the thin film covering the auxiliary member, to form a firstfiber reinforced plastic composite material layer; laminating anotherfiber reinforced plastic composite material having an elastic modulussmaller than that of the fiber reinforced plastic composite material ofthe first fiber reinforced plastic composite material layer, on theformed first fiber reinforced plastic composite material layer, to forma second fiber reinforced plastic composite material layer; laminatinganother fiber reinforced plastic composite material the same as that ofthe first fiber reinforced plastic composite material layer, on theformed second fiber reinforced plastic composite material layer, to forma third fiber reinforced plastic composite material layer; laminatinganother fiber reinforced plastic composite material the same as that ofthe second fiber reinforced plastic composite material layer and anotherfiber reinforced plastic composite material the same as that of thethird fiber reinforced plastic composite material layer, alternately bya predetermined times, on the formed third fiber reinforced plasticcomposite material layer; compaction-processing all the laminated fiberreinforced plastic composite material layers under second heatingconditions at a temperature lower than and for a time shorter than thoseof the first heating conditions, to form a strength member; laminatinganother fiber reinforced plastic composite material the same as that ofthe second fiber reinforced plastic composite material layer and anotherfiber reinforced plastic composite material the same as that of thethird fiber reinforced plastic composite material layer, alternately bya predetermined times, on the formed strength member;compaction-processing all the laminated fiber reinforced plasticcomposite material layers under the second heating conditions, to formanother strength member; laminating another fiber reinforced plasticcomposite material the same as that of the second fiber reinforcedplastic composite material layer and another fiber reinforced plasticcomposite material the same as that of the third fiber reinforcedplastic composite material layer, alternately by a predetermined times,on the formed strength member, to form a thick-walled cylindrical bodyhaving a predetermined thickness on the formed strength member; andheat-curing all the laminated fiber reinforced plastic compositematerial layers under the first heating conditions.

Further, the present invention provides a thick-walled cylindrical partmanufactured by the fiber reinforced plastic composite material whichincludes a plurality of sorts of fiber reinforced plastic compositematerials which have a different elastic modulus and are alternatelylaminated respectively.

In the method of manufacturing the thick-walled cylindrical part bycomposite material according to the present invention, in order toreduce the internal stress generated in the fiber reinforced plasticcomposite material layer after heat curing, when the major material ofthe thick-walled cylindrical part is a carbon fiber reinforced plasticcomposite material, a cushioning material (e.g., glass or aramide fiberreinforced plastic composite material) having an elastic modulus smallerthan that of the carbon fiber reinforced composite material is laminatedseparately about several to 20% being divided into several layers in thewall thickness direction. By these lamination layers, it is possible toreduce the internal stress generated in each layer and thereby toeliminate the interlayer separation caused after heat curing of thecylindrical part.

Further, during the lay-up processing, the laminated cylindrical part isprocessed for a compaction method at a temperature (e.g., 60° C. to 130°C.) lower than the curing temperature (e.g., 180° C.) for a time (e.g.,30 to 60 min.) and under pressure (e.g., vacuum to 7 kgf/cm²); that is,under such conditions that no harmful influence is exerted upon thephysical properties of the finally cured cylindrical part. By thiscompaction process, it is possible to reduce a change in the wallthickness thereof between the conditions when laid-up and after heatingand to prevent the occurrence of local meandering and local wrinklesproduced after heated for curing; that is, to decrease the internalstress.

Further, since the auxiliary member formed by the fiber reinforcedplastic composite material layer having a small thermal expansioncoefficient in the fiber direction is laminated inside the strengthmember required to increase the strength and the rigidity, it ispossible to prevent the inner layers from being shrunk after thestrength member is once heated for curing and then cooled, so that theinterlayer separation of the thick-walled cylindrical part can beprevented. Here, as the composite material used for this purpose, thecarbon fiber reinforced plastic composite material having a roughly zerothermal expansion coefficient in the fiber direction is suitably used.

Further, since the occurrence of the internal stress is proportional tothe difference between the curing temperature and the room temperature,it is possible to reduce the temperature difference between theconditions when heated for curing and when cooled by reducing the curingtemperature within such a range that the performance is not degraded ascompared with the case obtained in the conventional curing cycle. As aresult, it is possible to reduce the internal stress after the heatcuring.

Further, according to the wall thickness and the usage, it is possibleto suppress the occurrence of the internal stress by changing thelamination direction of the fiber reinforced plastic composite material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a mandrel used for the method ofmanufacturing a thick-walled cylinder part by fiber reinforced plasticcomposite material according to the present invention;

FIG. 2 is an illustration for assistance in explaining a first processof manufacturing the thick-walled cylinder part by the fiber reinforcedplastic composite material according to the present invention;

FIG. 3 is an illustration for assistance in explaining a second processof manufacturing the thick-walled cylinder part by the fiber reinforcedplastic composite material according to the present invention;

FIG. 4 is an illustration for assistance in explaining a third processof manufacturing the thick-walled cylinder part by the fiber reinforcedplastic composite material according to the present invention;

FIG. 5 is an illustration for assistance in explaining a fourth processof manufacturing the thick-walled cylinder part by the fiber reinforcedplastic composite material according to the present invention;

FIG. 6 is a graphical representation showing a curing cycle of themethod of manufacturing the thick-walled cylinder part by the fiberreinforced plastic composite material according to the presentinvention; and

FIG. 7 is a graphical representation showing analysis results of theinternal stress of the thick-walled cylinder part manufactured by thefiber reinforced plastic composite material according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described hereinbelow with reference tothe attached drawings.

FIG. 1 shows a forming mandrel used for the method of forming athick-walled cylinder part by a fiber reinforced plastic compositematerial according to the present invention. The mandrel 1 is formed ofsteel material (thermal expansion coefficient: 10 to 12×10⁻⁶/°C.).Further, the forming mandrel 1 is formed with a small taper extendingfrom one end to the other end thereof on an outer surface 1 a thereof,to facilitate removal of the cylindrical parts from the mandrel 1 afterheat curing.

As shown in FIG. 2, a carbon fiber reinforced plastic composite material(CFRP) 2 a is laid up on the outer surface 1 a of the forming mandrel 1at an angle θ (about 90 degrees) and with a radial thickness of aboutseveral millimeters (about 3 to 5 mm) in such a way that the wallthickness can be changed so as to cancel the tapered surface on theouter surface 1 a of the forming mandrel 1. The carbon fiber reinforcedplastic composite material (CFRP) 2 a laid up on the outer surface 1 aof the forming mandrel 1 is heated for curing (i.e., hot setting) in acuring cycle as shown in FIG. 6; that is, at 165° C. for 240 min.. Theheated carbon fiber reinforced composite material 2 a is formed as anauxiliary member 2. The conventional curing cycle (e.g., at 180° C. for120 min.) can be adopted, instead of the curing cycle shown in FIG. 6.

On the auxiliary member 2 laid up on the forming mandrel 1, a thin film(not shown) of high heat resistance (e.g., Teflon tape (“Teflon” is thetrademark for polytetrafluoroethylene)) is wound so as to cover all overthe surface of the auxiliary member 2. This thin film is used toperfectly separate the auxiliary member 2 from a strength member 3 to belaid up on the auxiliary member 2.

When the laminating direction of the carbon fiber reinforced plasticcomposite material of the strength member 3 differs, the thermalexpansion coefficient thereof differs according to the fiber directionof the carbon fiber reinforced plastic composite material. For instance,in the case of the carbon fiber reinforced plastic composite material,the thermal expansion coefficient in the fiber extending direction isalmost zero due to a strong influence of the carbon fiber. However,since the influence of the carbon fiber is weak in the directionperpendicular to the carbon fiber, the thermal expansion coefficient inthis perpendicular direction is relatively large due to a stronginfluence of the matrix resin. Therefore, when the carbon fiberreinforced plastic composite material is cooled from the curingtemperature to the room temperature, as far as there exists a differencein the lamination direction between the formed strength members 3, theinternal stress (strain) increases due to difference in thermalexpansion between the strength members 3, so that there exists the casewhere the strength members 3 are separated from each other. Therefore,it is possible to obtain cylindrical parts having a thicker wall bydecreasing the difference in the laminating direction between thestrength members 3.

The strength members 3 laid-up on the auxiliary member 2 can be formedin accordance with the three-stage process as shown in FIGS. 3 to 5.

In more detail, as shown in FIG. 3, on the auxiliary member (e.g.,Teflon tape (“Teflon” is the trademark for polytetrafluoroethylene)) 2laid up on the forming mandrel 1, a strength member 3 a (whichcorresponds to ⅓of all the plies) composed of the carbon fiberreinforced plastic composite material and a glass fiber reinforcedplastic composite material (as a cushioning composite material) is laidup in the laminating direction of ±17 degrees with respect to the axialline of the forming mandrel 1.

In the case where the external force applied to the cylindrical axis isalmost bending, tension and compression without including torsion, itmay be considered that the cylindrical part of high strength can beobtained when the laminating direction is determined nearly in the axialdirection. In this case, however, it is difficult to conduct thelamination work of the fiber reinforced plastic composite material.Here, as far as the strength and the rigidity can be both secured, it ispreferable to determine the laminating direction away from the axialdirection from the standpoint of the productivity. Therefore, a uniformlamination direction of ±17 degrees was set on condition that thenecessary strength and necessary rigidity can be both secured andfurther the lamination work can be facilitated under a given condition.However, without being limited only to this angle, this laminatingdirection can be changed at need.

The proportion of the carbon fiber reinforced plastic composite materialas a major material and the glass fiber reinforced plastic compositematerial as a cushioning material can be decided in accordance with acomplex rule so as to satisfy the required strength and elastic modulus.

In the case of the carbon fiber reinforced plastic composite materialand the glass fiber reinforced plastic composite material, there existsa small difference in strength between both. However, there exists a bigdifference in elastic modulus between both. Therefore, the ratio of thecarbon fiber reinforced plastic composite material to the glass fiberreinforced plastic composite material was determined as 9:1, inaccordance with the following complex rule of the elastic modulus, sothat the elastic modulus can satisfy the requested value:

E=Er×Vr+Eb×Vb

where E=requested elastic modulus

Er=elastic modulus of strength member

Eb=elastic modulus of cushioning material

Vr=volumetric proportion of strength member

Vb=volumetric proportion of cushioning material

The strength member 3 a laid up on the auxiliary member 2 of the formingmandrel 1 is processed for compaction at 100° C. under 6 kgf/cm² for 30min., in order to secure the cylindrical shape and to prevent theoccurrence of the local meandering and local wrinkles.

After that, as shown in FIG. 4, on the strength member 3 a laid up onthe forming mandrel 1, another strength member 3 b of about ⅓ of all theplies is further laid up. The strength member 3 b laid up on thestrength member 3 a is processed for compaction at 100° C. under 6kgf/cm² for 30 min., in order to secure the cylindricity and to preventthe occurrence of the local meandering and local wrinkles.

Further, as shown in FIG. 5, on the strength member 3 b laid up on theforming mandrel 1, the other strength member 3 c of about ⅓ of all theplies is further laid up. The strength member 3 c laid up on thestrength member 3 b is heated for curing at 165°0 C. for 240 min., inorder to obtain a cylindrical part having a thick wall and manufacturedby the carbon fiber reinforced plastic composite material.

The above-mentioned compaction conditions (pressure, temperature, time,the number of times) are determined within a range in which no harmfulinfluence is exerted upon the physical properties of the cylindricalpart having a thick wall manufactured by the composite material andcured finally.

As described above, in the above-mentioned preferred embodiment of themanufacturing method according to the present invention, when thestrength member 3 is formed, the fiber reinforced plastic compositematerial for forming the strength member 3 is laminated three timesseparately. Here, one layer of the glass fiber reinforced plasticcomposite material is laid up between the fiber reinforced plasticcomposite material at regular intervals. In addition, after the firstand second lamination process, the strength member 3 is processed forcompaction at 100° C. under 6 kgf/cm² for 30 min..

Further, in the preferred embodiment of the manufacturing methodaccording to the present invention, the number of the laminations of thestrength members 3 and the compaction processing timings are as follows:

8-laminations of the fiber reinforced plastic compositematerial→1-lamination of the glass fiber reinforced plastic compositematerial→9-laminations of the fiber reinforced plastic compositematerial→1-lamination of the glass fiber reinforced plastic compositematerial→8-laminations of the fiber reinforced plastic compositematerial→compaction processing

→1-lamination of the fiber reinforced plastic compositematerial→1lamination of the glass fiber reinforced plastic compositematerial→9-laminations of the fiber reinforced plastic compositematerial→1-lamination of the glass fiber reinforced plastic compositematerial→9-laminations of the fiber reinforced plastic compositematerial→1-lamination of the glass fiber reinforced plastic compositematerial→5-laminations of the fiber reinforced plastic compositematerial→compaction processing

→4-laminations of the fiber reinforced plastic compositematerial→1-lamination of the glass fiber reinforced plastic compositematerial→9-laminations of the fiber reinforced plastic compositematerial→1-lamination of the glass fiber reinforced plastic compositematerial→9-laminations of the fiber reinforced plastic compositematerial→1-lamination of the glass fiber reinforced plastic compositematerial→3-laminations of the fiber reinforced plastic compositematerial→heat curing processing.

In this embodiment, after the third lamination, the cylindrical part washeated for curing at 165° C. under 6 kgf/cm² for 240 min. Thistemperature condition is lower than that of the conventional conditionsas 180° C. under 6 kgf/cm² for 120 min.. Since the heat curingtemperature is lowered, the difference between the heating temperatureand the room temperature can be reduced, so that the thermal stress canbe decreased. Further, it was confirmed that the performance of thecomposite material is not changed due to the change in curingconditions. In more details, test pieces were heat-cured at 165° C. for240 min., and further it was confirmed that these test pieces were notchanged at the glass transition point temperature. Further, it wasconfirmed that the non-reactive substance contained in the test piecewas equivalent to that of a test piece cured at 180° C. for 120 min., bymeasuring the water absorption quantity of these test pieces. Inaddition, the same test pieces to each of which the final heat-curingprocess was made were tested for strength. It was confirmed that thestrength was not reduced. On the basis of the above-mentionedconfirmations, the final heat-curing conditions were decided.

The above-mentioned compaction processing is made to secure the truecylindrical shape and to prevent the occurrence of local meandering andlocal wrinkles. These conditions can be decided within a range where thephysical properties of the composite material do not deteriorate afterthe final heat curing, on the basis of such a temperature standard thatthe plastic begins to flow and such time standard that the plastic isnot yet cured by heat. In other words, the conditions of the compactionprocessing decided on the basis of the property examination of theplastic after compaction processing and the strength test results of theplastic after the final heat-curing. The decided compaction conditionsare as follows: the temperature is 60 to 130° C., and the pressure is 3to 6 kgf/cm² of the ordinary heat curing conditions.

Table 1 lists the relationship between the curing conditions and thephysical properties.

TABLE 1 CURING CONDITIONS AND PROPERTIES GLASS WATER BENDING BENDINGTRANSIT ABSORB CURING STRENGTH MODULUS TEMP RATIO CONDITIONS (kgf/mm²)(kgf/mm²) Tg (° C.) (%) 180° C. × 120 min. 213 12,300 195 0.43 165° C. ×240 min. 206 12,300 191 0.41

On the basis of the above-mentioned measurement results, in the curingcycle of the present invention (curing time: 240 min.; curing temp: 165° C.), the performance equivalent to that of the conventional curingcycle (curing time: 120 min.; curing temp: 180 ° C.) was obtained. As aresult, it was possible to reduce the temperature difference between thecuring temperature and the room temperature.

In the thick-walled cylindrical part manufactured by fiber reinforcedplastic composite material according to the present invention, the majormaterial is the carbon fiber reinforced plastic (CFRP) and thecushioning material is glass fiber reinforced plastic (GFRP). Theproportion of both is 9:1 on the basis of the requirement of strengthand rigidity. Further, the lamination orientation is of unidirection of±17° (100%). This unidirectional lamination orientation has the bendingstrength and the rigidity both equivalent to those of the cylindricalparts manufactured by the composite material having the laminationorientation of ±10° (65%)/±45° (25%)/±85° (10%).

FIG. 7 shows the analysis results (NASTRAN) of the internal stress ofthe thick-walled cylindrical part manufactured by composite material,which are obtained after cured in the curing cycle.

In FIG. 7, a solid curve shows an internal stress change obtained by thethick-walled cylindrical part manufactured by composite material havingthe lamination orientation of the unidirection of ±17° (100%) and thecuring temperature of 165° C.; a dashed-line curve shows an internalstress change obtained by the thick-walled cylindrical part manufacturedby composite material having the lamination orientation of ±10°(65%)/±45° (25%)/±85° (10%) and the curing temperature of 180° C.; and adot-dashed-line curve shows an internal stress change obtained by thethick-walled cylindrical part manufactured by composite material havingthe lamination orientation of ±10° (65%)/±45° (25%)/±85° (10%) and thecuring temperature of 165° C.

Here, the proportion of the carbon fiber reinforced plastic compositematerial to the glass fiber reinforced plastic composite material bothfor forming the lamination orientation of the thick-walled cylindricalpart manufactured by composite material is 9:1.

In the thick-walled cylindrical part manufactured by composite materialhaving the lamination orientation of ±10° (65%)/±45° (25%)/±85° (10%),the lamination directions of ±10° and ±45° are applied to the carbonfiber reinforced plastic composite material and the laminating directionof ±85° is applied to the glass fiber reinforced plastic compositematerial. Further, the number of the laminations and the timings of thecompaction process are as follows:

±10° 5-laminations→±45° 1-lamination→±85° 1-lamination→±45°1-lamination→±10° 6-laminations→±45° 1-lamination→±85° 1-layer→±45°1-lamination→±10° 6-laminations→±45° 1-lamination→85° 1-layer→±45°1-lamination→10° 2-laminations→compaction

→±10° 4-laminations→±45° 1-lamination→±85° 1-lamination→±45°1-lamination→±10° 6-laminations→±45°1-lamination→±85° 1-lamination→±45°1-lamination→±10° 6-laminations→±45° 1-lamination→±85° 1-lamination→±45°1-lamination→10° 2-laminations→compaction

→±10° 4-laminations→±45°1-lamination→±85° 1-lamination→±45°1-lamination→±10° 6-laminations→±45° 1-lamination→±85° 1-lamination→±45°1-lamination→±10° 6-laminations→±45° 1-lamination→85° 1-lamination→45°3-laminations→final curing

FIG. 7 indicates that in the case of the thick-walled cylindrical partmanufactured by composite material as shown by the solid line curve, itis possible to reduce the internal stress largely by reducing the curingtemperature and by determining only one laminating direction.

Table 2 lists the experimental results of the interlayer separation ofthe thick-walled cylindrical part manufactured by the method accordingto the present invention, in comparison with those of the interlayerseparation manufactured by the other methods.

TABLE 2 PRESENCE OR ABSENCE OF INTERLAYER SEPARATION ACCORDING TOMANUFACTURING METHODS LAMINATION NO T A B C D ORIENTATION E 1 11 NO NONO 180 ±10°/±45°/±85° NO 2 30 NO NO NO 180 ±10°/±45°/±85° YES 3 30 YESYES NO 180 ±10°/±45°/±85° NO 4 42 YES YES NO 180 ±10°/±45°/±85° YES 5 42YES YES YES 165 ±10°/±45°/±85° YES 6 42 YES YES YES 165 ±17° NO T:THICKNESS (mm) A: APPLICATION OF CUSHIONING MATERIAL B: APPLICATION OFHEAT COMPACTION C: APPLICATION OF AUXILIARY MEMBER D: CURING TEMPERATURE(° C.) E: PRESENCE OF INTERLAYER SEPARATION YES: APPLIED, NO: NOTAPPLIED

The above-mentioned experiment results indicate that in the case of thewall thickness of 11 mm (No. 1), the interlayer separation did not occurwhen no special method was adopted.

In the case of the wall thickness of 30 mm (No. 2), the interlayerseparation occurred at roughly the middle of the wall thickness.

In the case of the wall thickness of 30 mm (No. 3), the interlayerseparation did not occur because the cushioning material was applied andfurther the heat compaction process was made.

In this case, the number of the laminated laminations of the strengthmember of the thick-walled cylindrical part and the timing of thecompaction processing were as follows: Further, the laminatingdirections of ±10° and ±45° were applied to the carbon fiber reinforcedplastic composite material and the lamination direction of ±85° wasapplied to the glass fiber reinforced plastic composite material.

±10° 5-layers→±45° 1-layer → 85° 1-layer → ±45° 1-layer ±10°6-layers→±45° 1-layer→±85° 1-layer→±45° 1-layer→±10° 6-layers→±45°1-layer→±85°1-layer→±45° 1-layer→10° 2-layers→compaction

→±10° 4-layers→±45° 1-layer→±85° 1-layer→±45° 1-layer→±10° 6-layers→±45°1-layer→±85° 1-layer→±45° 1-layer→±10° 6-layers→±45° 1-layer→±85°1-layer→±45° 1-layer→±10° 2-layers final curing

Further, in the case of the wall thickness of 42 mm (No. 4), althoughthe cushioning material was applied and further the heat compaction wasmade, the interlayer separation occurred almost all over thecircumference and length thereof at roughly the middle of the wallthickness.

In the case of the wall thickness of 42 mm (No. 5), although thecushioning material was applied; the heat compaction process was made;the auxiliary member was applied; and further the curing temperature waslowered from 180° C. to 165° C., the interlayer separation occurredlocally.

Further, the number of laminated layers and the compaction timing of thewall thickness of 42 mm (No. 4 and No. 5) are the same as with the caseshown by the dashed curve or the dot-dashed curve line in FIG. 7.

In the case of the wall thickness of 42 mm (No. 6) according to thepresent invention, the laminating orientation was of unidirection of±17°; the cushioning material was applied; the heat compaction processwas made; the auxiliary member was applied; and further the curingtemperature was lowered to 165° C. Therefore, it was possible to obtainthe cylindrical parts of excellent quality having no interlayerseparation.

Further, in the case of such a laminating method that: the carbon fiberreinforced plastic composite material having the laminating directionsof ±10° and ±45° and the glass fiber reinforced plastic compositematerial having the laminating direction of ±85° are combined with theheat compaction process, without use of the unidirectional lamination;the auxiliary member is not used; and the final heat curing temperatureis not changed, it is possible to obtain the 30 -mm thick cylindricalpart having no interlayer separation. In this cylindrical parts, sincethe carbon fiber is arranged in the laminating direction of ±45°, thethick-walled cylindrical part is strong against both the bending andtorsion.

The present invention has been explained by taking the case where theinternal diameter of the cylindrical part is decoded as 80 mm (radius:40 mm) as shown in FIG. 7. However, the limit of the wall thickness isnot yet confirmed. Therefore, when the limit of the wall thickness isconfirmed, it may be possible to obtain the thick-walled cylindricalpart other than those as listed in Table 2. Further, when the internaldiameter of the cylindrical part changes, even if the wall thickness isnot changed, the internal stress differs. Therefore, when themanufacturing method according to the present invention is adopted bychanging the internal diameter of the cylindrical part, it may bepossible to obtain the cylindrical part having the wall thicknesspartially different from the values as listed in Table 2. For instance,when the internal diameter is larger than 80 mm, since the internalstress is reduced, it is possible to obtain the cylindrical part havingthe wall thickness larger than that obtained conventionally when theinternal diameter is 80 mm. Therefore, the technical scope of thepresent invention includes the manufacturing method in which theinternal diameter is changed, without being limited to only the internaldiameter of 80 mm.

As described above, in the method according to the present invention, itis possible to manufacture the thick-walled cylindrical part having anexcellent quality, by using the fiber reinforced plastic compositematerial, and by reducing the internal stress generated after the heatcuring process.

While the presently preferred embodiments of the present invention havebeen shown and described, it is to be understood that the disclosuresare for the purpose of illustration and that various changes andmodification may be made without departing from the scope of theinvention as set forth in the appended claims.

What is claimed is:
 1. A method of manufacturing a cylindrically-shapedarticle, comprising: (a) winding a first fiber reinforced plasticsmaterial having a first elastic modulus onto a mandrel to form at leastone layer of the first fiber reinforced plastics material; (b) winding asecond fiber reinforced plastics material having a second elasticmodulus less than the first elastic modulus onto the at least one layerof the first fiber reinforced plastics material to form at least onelayer of the second fiber reinforced plastics material, such that anumber of layers of the first fiber reinforced plastics material isequal to or greater than a number of layers of the second fiberreinforced plastics material; and (c) repeating steps (a) and (b) atleast once to thereby form subsequent layers of the first and secondfiber reinforced plastics materials, wherein the first and second fiberreinforced plastics materials are wound at an angle of approximately±17° with respect to an axial direction of the mandrel for forming theinternal diameter of the cylindrical part with at least 40 mm thickness.2. A method of manufacturing a cylindrically-shaped article with a firstfiber reinforced plastic material having a first elastic modulus and asecond fiber reinforced plastic material having a second elastic modulusless than the first elastic modulus, said method comprising the stepsof: laminating five laminations of the first fiber reinforced plasticmaterial at a laminating direction of ±10° to an axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating onelamination of the second fiber reinforced plastic material time at alaminating direction of ±85° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating sixlaminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating onelamination of the second fiber reinforced plastic material at alaminating direction of ±85° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating sixlaminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating onelamination of the second fiber reinforced plastic material at alaminating direction of ±85° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating twolaminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylidrically-shaped article; executing a compaction process; laminatingfour laminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylindrically-shaped article; laminating the one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating onelamination of the second fiber reinforced plastic material at alaminating direction of ±85° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45to theaxial direction of the cylindrically-shaped article; laminating sixlaminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating onelamination of the second fiber reinforced plastic material at alaminating direction of ±85° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating sixlaminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating onelamination of the second fiber reinforced plastic material at alaminating; direction of ±85° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating twolaminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylindrically-shaped article; executing a compaction process; laminatingfour laminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating onelamination of the second fiber reinforced plastic material at alaminating direction of ±85° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating sixlaminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating onelamination of the second fiber reinforced plastic material at alaminating direction of ±85° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating sixlaminations of the first fiber reinforced plastic material at alaminating direction of ±10° to the axial direction of thecylindrically-shaped article; laminating one lamination of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; laminating onelamination of the second fiber reinforced plastic material at alaminating direction of ±85° to the axial direction of thecylindrically-shaped article; laminating three laminations of the firstfiber reinforced plastic material at a laminating direction of ±45° tothe axial direction of the cylindrically-shaped article; and executing afinal curing, such that 65% of the laminations are oriented at ±10° tothe axial direction of the cylindrically-shaped article, 25% of thelaminations are oriented at ±45° to the axial direction of thecylindrically-shaped article, and 10% of the laminations are oriented at±85° to the axial direction of the cylindrically-shaped article.
 3. Amethod of manufacturing a cylindrical-shaped article, comprising: (a)winding a first fiber reinforced plastics material having a firstelastic modulus onto a mandrel to form at least one layer of the firstfiber reinforced plastics material; (b) winding a second fiberreinforced plastics material having a second elastic modulus less thanthe first elastic modulus onto the at least one layer of the first fiberreinforced plastics material to form at least one layer of the secondfiber reinforced plastics material, such that a number of layers of thefirst fiber reinforced plastics material is equal to or greater than anumber of layers of the second fiber reinforced plastics material; and(c) repeating steps (a) and (b) at least once to thereby form subsequentlayers of the first and second fiber reinforced plastics materials,wherein the first reinforced plastics material is wound at an angle ofapproximately 10° and ±45° with respect to an axial direction of themandrel, the second fiber reinforced plastics material is wound at anangle of approximately ±85° with respect to an axial direction of themandrel for forming the cylindrical part with at least 30 mm thickness.4. A method of manufacturing a cylindrical-shaped article with a firstfiber reinforced plastic material having a first elastic modulus and asecond fiber reinforced plastic material having a second elastic modulusless than the first elastic modulus, said method comprising the step of:laminating eight laminations of the first fiber reinforced plasticmaterial; laminating one laminations of the second fiber reinforcedplastic material; laminating nine laminations of the first fiberreinforced plastic material; laminating one lamination of the secondfiber reinforced plastic material; laminating eight laminations of thefirst fiber reinforced plastic material; executing a compaction process;laminating one lamination of the first fiber reinforced plasticmaterial; laminating one lamination of the second fiber reinforcedplastic material; laminating nine laminations of the first fiberreinforced plastic material; laminating one lamination of the secondfiber reinforced plastic material; laminating nine laminations of thefirst fiber reinforced plastic material; laminating one lamination ofthe second fiber reinforced plastic material; laminating fivelaminations of the first fiber reinforced plastic material; executing acompaction process; laminating four laminations of the first fiberreinforced plastic material; laminating one lamination of the secondfiber reinforced plastic material; laminating nine laminations of thefirst fiber reinforced plastic material; laminating one lamination ofthe second fiber reinforced plastic material; laminating ninelaminations of the first fiber reinforced plastic material; laminatingone lamination of the second fiber reinforced plastic material;laminating three laminations of the first fiber reinforced plasticmaterial; and executing a final curing, the first and second reinforcedplastic materials are wound at a laminating direction of ±17° to theaxial direction of the cylindrically-shaped article.